Conventionally, an active-matrix substrate, which is provided with pixel electrodes and switching elements disposed in a two-dimensional manner, finds wide application in devices such as a display device and a capturing device. For example, demand for the active matrix substrate as monitors for an audio/visual device and an office automation device has been rapidly increasing. Examples of such a display device and a capturing device include liquid crystal display devices (LCDs: Liquid Crystal Displays), which are expected for application to a flat TV, and x-ray capturing devices (FPXDs: Flat Panel X-ray Detectors), which are capable of directly reading out x-ray images in the form of electric signals without an film.
The active matrix substrate for use in such a display device and a capturing device includes thin film transistors (TFTs) of metal wiring and semiconductor, which are precisely arrayed in a matrix pattern on an insulating substrate such as a glass substrate. Manufacture of the active matrix substrate requires highly sophisticated processing techniques such as photolithography and expensive manufacturing equipment. This has made it difficult to manufacture a large-area active-matrix substrate because the yield dropped drastically as the area or resolution of the active-matrix substrate was increased. Another problem is that once the manufacturing equipment is built, it is impossible to manufacture an active-matrix substrate which is larger than the substrate size suitable for the manufacturing equipment. That is, it has been difficult to manufacture a large active-matrix substrate to accommodate the increased size of display devices or capturing devices.
As a counter-measure for these problems, there have been proposed methods of forming a composite active-matrix substrate by connecting a plurality of small active-matrix substrates. For example, “Large Area Liquid Crystal Display Realized by Tiling of Four Back Panels (Proceedings of the 15th International Display Research Conference (ASIA DISPLAY '95, pp. 201–204 (1995)))” (reference 1) discloses an arrangement of a composite active-matrix substrate for use in liquid crystal display devices. Further, U.S. Pat. No. 5,827,757 (reference 2), published on Oct. 27, 1998, discloses a method for manufacturing a composite active-matrix substrate and an x-ray capturing device utilizing the composite active-matrix substrate.
The active-matrix substrate described in the above reference 1, as shown in FIGS. 13(a) through 13(c), is fabricated as follows: after four small active-matrix substrates 101, with their element bearing sides 101a facing down, are aligned on a stage 103 with a vacuum chuck, a back side (upper side in FIG. 13(a)) of the active-matrix substrates 101 is bonded to a base substrate 102 with an adhesive resin 105. Here, the adhesive resin 105 contains a spacer 104. Further, an ultraviolet curable resin is used for the adhesive resin 105.
Meanwhile, the composite active-matrix substrate described in the above reference 2, as shown in FIGS. 14(a) through 14(g), is made up of a plurality of small active-matrix substrates 111 bonded to a base substrate 112. Specifically, this composite active-matrix substrate is fabricated in the following manner: after an edge of the active-matrix substrate 111 whose element bearing side is covered with a protecting film 121 is cut by dicing and polished (see FIGS. 14(a) and 14(b)), the plurality of active-matrix substrates 111, with their element bearing sides facing down, are aligned on a stage 113 and connected to each other with an adhesive resin 141 which fills a gap between the active-matrix substrates 111 (see FIGS. 14(c) and 14(d)). Thereafter, a back side (upper side in FIG. 14(d)) of the plurality of active-matrix substrates 111 is bonded to a base substrate 112 with an adhesive resin 131. Then, after the active-matrix substrates 111 are removed from the stage 113, the protecting film 121 is peeled off from the active-matrix substrates 111 (see FIGS. 14(e) through 14(g)). Here, formation of a large number of orderly openings (holes for releasing an adhesive resin) 112a prevents air bubbles from being trapped in the adhesive resin 131 which fills a spacing between the active-matrix substrate 111 and the base substrate 112, and helps excess adhesive resin 131 to escape.
However, the foregoing conventional composite active-matrix substrates and manufacturing methods have the following problems. For example, the composite active-matrix substrate described in the reference 1 appears to be manufactured in such a way that the plurality of active-matrix substrates 101 aligned together, coated with the adhesive resin 105 having fluidity, are bonded to the base substrate 102. Here, the plurality of active-matrix substrates 101 must be bonded with the base substrate 102 in a state where a distance between these two substrates is at the distance of a gap determined by a spacer. This causes a problem that the adhesive resin 105 seeps out (pressed out) of the active-matrix substrate 101. As a result, it becomes difficult to prevent air bubbles from being trapped in the adhesive resin 105, and cleaning of the excess adhesive resin 105 will be required. This results in a problem that workability suffers significantly.
On the other hand, in the composite active-matrix substrate described in the above reference 2, theoretically, a large number of openings 112a formed in advance on the base substrate 112 can prevent air bubbles from being trapped, and excess adhesive resin 131 can escape through the openings 112a when the base substrate 112 and the active-matrix substrate 111 are bonded. However, in cases where a comparatively large composite active-matrix substrate is to be manufactured, the base substrate 112 cannot be pressed down (toward the active-matrix substrate 111) uniformly over the surface when it is bonded. This results in a problem that air bubbles and the adhesive resin 131 cannot be released properly at portions of the base substrate 112 where the applied pressure is weaker, or at thinner portions of the base substrate 112. In addition, forming the large number of openings 112a on the base substrate 112 increases manufacturing costs. Further, cleaning of excess adhesive resin 131 which has seeped out through the opening 112a is still required, resulting in a problem that workability suffers significantly.
Further, in the composite active-matrix substrate described in the above reference 2, a rubber squeegee (not shown) is used to fill a gap between the small active-matrix substrates 111 with the adhesive resin 141. This causes problems that the adhesive resin 141 is likely to spread to the top surface (element bearing side) of the active-matrix substrate 111, and an external force is applied to the active-matrix substrate 111 through the rubber squeegee. Thus, filling of the adhesive resin 141 required an extremely thick protecting film 121 which covered the top surface of the active-matrix substrate 111.